Typically, a search engine utilizes a ranking function to predict the degree of relevance of a document to a particular query. The ranking function takes multiple features from the document as inputs and computes a number that allows the search engine to sort the documents by predicted relevance. The ranking function (including its parameters) may be built into the search engine, or the search engine may allow the specification of multiple custom ranking functions. However, extensive and sophisticated customization of ranking models by the average administrator is non-existent.